>>16,18
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https://pubs.acs.org/doi/10.1021/acs.est.5c05711

An additional challenge in REE processing from both primary and secondary sources is the presence of uranium and thorium, typically referred to as Naturally Occurring Radioactive Materials (NORMs). These elements are frequently colocated with the rare earth minerals due to their similar chemical structure, leading to radiation concerns during extraction. Although NORM concentration in coal waste is usually low, concentrating REEs in a leach solution can lead to simultaneous concentration of these radioactive elements, thereby increasing waste management complexity and safety concerns in the downstream separation lines.